1. Field of the Invention
The present invention relates to a spin valve read head with plasma produced metal oxide insulation layer between lead and shield layers and, more particularly to a read head that caps first and second lead layers with a metallic oxide layer that, in combination with a gap layer, provides electrical insulation between the lead layers and a shield layer so as to prevent electrical shorts therebetween, and a method of making the read head.
2. Description of Related Art
A read head includes a sensor that is located between first and second non-magnetic gap layers which, in turn, are located between first and second shield layers. The resistance of the sensor changes in response to magnetic fields in the tracks of a rotating disk. A sense current conducted through the sensor results in voltage changes that are detected by processing circuitry as readback signals. The sensor may be a spin valve sensor or an anisotropic magnetoresistive (AMR) sensor. A spin valve sensor, which is preferred, includes a spacer layer that is located between a pinned layer and a free layer, and an antiferromagnetic layer that pins the magnetic moment of the pinned layer. An AMR sensor includes a ferromagnetic stripe. First and second lead layers are connected to side edges of either sensor for conducting a sense current therethrough.
Each of the lead layers has an end edge that abuts a respective side edge of the sensor to form what is known in the art as a contiguous junction. The distance between the contiguous junctions defines the track width of the read head. A hard magnetic layer typically underlies each lead layer and also has an end edge that abuts a respective side edge of the sensor. The hard magnetic layer, known in the art as a hard bias layer, longitudinally biases the sensor to stabilize its magnetic domains so as to prevent Barkhausen noise. Alternatively, each lead layer may overlap a portion of the sensor to form what is known in the art as a continuous junction. The track width of a continuous junction read head is defined by the distance between the overlapping portions. The contiguous junction configuration is preferred to the continuous junction configuration because one masking step can be employed for defining the track width of the sensor as well as depositing the leads to make the contiguous junctions.
The areal or bit density of a read head is determined by its track width and read gap. Track width defines the number of tracks read per inch (track density), while read gap defines the number of bits read per inch of track (linear density). From these parameters, the bits read per square inch of recording surface can be determined. With regard to read head construction, track density is easier to increase than linear density. In order to maximize linear density, the first and second gap layers at the top and the bottom of the sensor must be extremely thin. For instance, for a 10 Gb/in.sup.2 read head, the total read gap should be about 150 nm. With a sensor thickness of about 35 nm, this leaves about 115 nm to be allocated between the first and second gap layers. However, a gap layer of 57 to 58 nm may not be sufficiently thick to protect a lead layer from electrical shorts. Because of the large area of the lead layers, there is a high risk that the adjacent gap layers will have pinholes that permit shorting. This has a serious impact on manufacturing yield.
One way to minimize the risk of pinhole shorts is to deposit additional insulation material outside the sensor frame. This can be accomplished by depositing a layer of insulation immediately on top of the first gap layer outside the sensor frame, and then depositing another layer of insulation outside the sensor frame just before the second gap layer is formed. This leaves only the first and second gap layers within the sensor frame, but thickens the insulation depth outside the sensor frame where the lead layers extend to the terminals. Unfortunately, a portion of each lead layer between a contiguous junction and the additional insulation layers is protected only by the first and second gap layers, which leaves that portion at risk of shorting to a shield layer. Another problem with this arrangement is that the additional insulation layers thermally insulate the sensor, thereby increasing the risk that heating of the sensor will alter its magnetic characteristic. A further drawback is that a masking step is required for each of the two additional insulation layers.